Implementation and study of dopant-assisted photoionization with a miniature capillary inlet ion trap mass...

Dopant-assisted photoionization (PI) has been widely used in the mass spectrometric analysis of volatile compounds. Exploring simple doping methods will benefit parameter optimization and promote the application of this technique.

A previously built miniature ion trap mass spectrometer was used to study dopant-assisted vacuum PI. The sampling system of this device was modified to provide three inlets for the simultaneous introduction of analytes, dopants, and auxiliary air. Then, dopant solution was directly injected into the ion trap chamber through a self-aspirating capillary inlet and rapidly evaporated without heating. Various dopant solutions were prepared and switched during the experiments.

When analyzing some aniline compounds, the signals of all analytes were improved by more than 10 times after the injection of 2% anisole solution as a dopant. In addition, anisole can provide analyte signals more than three times stronger than those provided by the other dopants. On the basis of the ionization energy selectivity of dopant-assisted PI, some isomers in the mass spectrometric analysis were distinguished using different additives.

In general, liquid doping is as feasible and as effective as other traditional methods, and using appropriate dopants with high PI efficiency or feeding more dopants contributes to the ionization of analytes. The proposed method also offers several unique merits, such as simple operation, low consumption, and smooth switching with minimal residue.